This invention relates to storage and retrieval of video information and, more particularly, to an apparatus and method which permits an image to be efficiently stored in an encoded fashion, and retrieved more quickly for display, recording and/or broadcast.
In various applications it is desirable to have frames of video information available for virtually instantaneous presentation upon command of an operator. For example, in the television broadcast field, it is advantageous to have a "library" of stored frames which represent relatively high quality pictures that might be used during a program; for example, a picture of an entertainment, political, or sports figure, or a table of statistics, or a graph or chart, etc. Pictures of this type can be generated beforehand, and stored on a bulk storage medium, such as a magnetic disk. In one method, a television camera is utilized to generate an analog video signal, which is then digitized and stored on a disk. Alternatively, a character generator can generate the video signal in analog form, and it can be converted to digital form, or it may be generated directly in digital form, and stored on disk. When it is desired to use the stored frame of video information, it can be read from the disk and stored in a frame buffer; i.e., an addressable block of random access memory which stores digital pixel values (color and/or luminence values) at addresses corresponding to each respective pixel position of a video frame. A video signal can then be scanned out of the frame buffer for real time presentation of live video. Of course, the output of the frame buffer can be first converted to an analog video signal, as desired.
A substantial drawback of the described technique is that in order to have almost immediate presentation of a selected image from the library of pictures on the disk, one must generally provide a high-speed high-density disk or other storage medium that is very expensive. When using lower cost disks, the operation of reading a frame of video from disk to frame buffer will be relatively slow.
It is among the objects of the present invention to provide an apparatus and method which permits fast access to stored frames of video without requiring expensive high-speed bulk storage media. It is also among the objects of the present invention to provide a technique which permits efficient encoding of video signal such that less storage room is required on a bulk storage medium; this being done in conjunction with an encoding and processing technique that is not unduly complex or expensive.